Auscultation forms an important part of clinical examination for screening patients with or suspected to have heart disease. Automatic identification of patterns in heart sounds is useful for assisted diagnosis. The beat to beat duration of the heart cycle varies in every individual and so do the cyclic content, for example, systolic duration and corresponding murmur. Heart sounds are often superimposed by noises including ambient noise and breathing noise, for example. For a more effective auscultation or for automatic analysis of heart sounds, it is important to identify the aperiodic noise and the periodic signals for better diagnosis. The breathing noise itself may be useful in reaching more accurate diagnosis and the presence of adequate amount of ambient noise may enhance signal perception by physicians.
The electronic processing of heart sound signals depends on some form of filtering to reduce the energy of noise in the overall signal. Even though the heart sound signals lie essentially below 200 Hz, for instance, some components lie above this frequency as well. Thus, using a low pass filter to improve the signal to noise ratio (SNR) of the heart sounds may not be the ideal way.
The document US 20080273709-A1 describes a device that processes heart sound signals, wherein an analysis tool includes an interaction tuner, a processing tuner and an output tuner. The interaction tuner includes a preset tuning selector and a dynamic range tuning selector. The processing tuner includes a band pass filter and an algorithmic extraction engine which applies extraction algorithms to the electric heart signals, segments them and extracts signals of interest.